If a decimal exponent is less than -309 return 0.0.
If a decimal exponent is greater than +324 return +infinity.

BUG=
TEST=

Review URL: http://codereview.chromium.org/3519017

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5623 ce2b1a6d-e550-0410-aec6-3dcde31c8c00